Numerical Modeling of Spark Ignition in Internal Combustion Engines

PhD thesis The aim of this work is to develop a new and comprehensive spark ignition model for 3D CFD combustion modeling in Spark Ignition (SI) engines. The literature review on the experimental and numerical investigations of the spark ignition shows that although this process is well-understood, its complexity makes its modeling a very challenging task. The detailed description of all the phenomena occurring during the spark ignition would require resolving very short time and length scales on very fine numerical meshes, which may not be practical in commercial engineering applications. Usually, simplified phenomenological models of the spark ignition and early flame propagation are developed. The review of the spark ignition models for 3D CFD combustion modeling reveals that in the individual models only particular aspects of the ignition phenomenon are described in detail, while others are taken into account in a very simplified way or even completely omitted. This shows that there is still space for improvements in the field of spark ignition modeling and it is desirable to develop new and more accurate ignition models. The ignition model for SI engines presented in this work integrates sub-models for individual phenomena of the spark ignition process. The sub-models for the electrical circuit of the ignition system, for the spark plasma dynamics, for the heat transfer from the spark towards surrounding mixture, for the ignition delay of the mixture and for the early flame kernel growth are coupled together to form one comprehensive ignition model. The model is implemented into the AVL FireTM CFD solver in the context of the Gequation combustion model and allows to predict the temporal development and deflection of the spark plasma channel, the ignition delay time and the position of the initial flame kernel. In comparison to other approaches, a more detailed physical model is developed to accurately describe each phenomenon and gain a more complete understanding of the spark ignition process in SI engines. The performance of the new model is numerically verified by comparing calculated results to experimental data in various cases. The results of the spark discharge modeling in a strong flow field confirm that the model correctly predicts the duration of the discharge process with multiple breakdowns, the deflection of the spark during the first breakdown of the spark arc, the current and the voltage in the electrical circuit and the energy supplied to the spark arc. The results of the spark ignition and combustion modeling in the AVL single cylinder research engine show that the flow field generated in the cylinder during the scavenging and compression processes can considerably deflect the spark arc during the ignition process. The new ignition model is capable of predicting the spark deflection and the actual ignition point dragged away from the spark electrodes. The numerical pressure profile in the cylinder and the Rate of Heat Release (ROHR) also matches the measurement with a good agreement, which proves that the ignition model correctly predicts the ignition process, while the combustion model provides correct flame propagation. Finally, the ignition model is used for modeling the ignition and flame propagation from two spark plugs in the PAMAR-4 Opposed-Piston research engine. The numerical pressure profile in the cylinder and the ROHR are again in agreement with the measurements which shows that the new ignition model is able to correctly predict the ignition of the air-fuel mixture from multiple spark plugs at discrete locations in the combustion chamber, while the G-equation combustion model can handle the flame propagation of the distinct flame fronts coming from multiple ignition pointsThe research was co-financed by Polish Ministry of Science within the frame of science support funds for international co-funded projects in 2016–201